pda_power: clean up irq, timer

Clean up pda_power interrupt handling:

Prior to this patch, the driver would pass information it needed
to the interrupt handler dev_id pointer, and then prompt forget it
ever did so, recreating that same information after a couple passes
through the timer-based state machine.

This patch removes the redundant checks by passing the
pda_power_supply[] pointer through the state machine.  The current
code passed 'irq' through the state machine, as an index to recreate
the pointer, when we could more simply pass around the pointer itself.

This patch makes it easier to remove the 'irq' argument in the future,
in addition to cleaning up the driver today.

Signed-off-by: Jeff Garzik <jeff@garzik.org>